It is known in the art to produce liquid hydrocarbon or lipid by fermentation. In such a fermentation process, micro-organisms are used to convert a suitable substrate into hydrocarbon, lipid or a mixture thereof. Such microbial production of hydrocarbon or lipid is for example used to produce biofuels. Furthermore, chemical intermediates and flavour or fragrance compounds may be produced in this way.
The fermentation mixture obtained by the fermentation process is a complex mixture comprising micro-organisms, substrate, nutrient, the liquid fermentation product (e.g. hydrocarbon or lipid) and the gaseous fermentation product (i.e. fermentation gas). The mixture is a four phase (S-G-L-L) mixture: microbial cells (solid), fermentation gas and/or other gases (gas), aqueous medium (liquid) and the hydrocarbon or lipid (liquid).
A problem encountered in the microbial production of hydrocarbon or lipid by fermentation is that it is difficult to separate the produced hydrocarbons and lipids from the complex fermentation mixture.
Separation of the hydrocarbon and lipid generally relies on the low water-miscibility of the lipids or hydrocarbon with the aqueous medium, as is also described in the following prior art.
EP 2 196 539 describes the use of different solid-liquid-liquid separation techniques to separate the lipid and hydrocarbon biofuels (BHC) from a fermentation mixture. Preferred steps for this include the use of flotation of the BHC using dissolved carbon dioxide and other components in the fermentation gas in combination with a ventury type device (or other pressure reduction devices) or the use of hydrocyclones. No gas is actively injected into the reactor.
WO 2007/139924 is directed to a method for producing and separating bio-organic compounds in a two-phase system, which system comprises an aqueous medium with host cells as a first layer and a liquid organic second phase comprising the bio-organic compound produced by the host cells. It mentions the production of gases such as carbon dioxide during or after the fermentation process, which may be vented off using a gas outlet. Many possible variants of the production method are described, including batch, continuous, fed-batch or semi-continuous fermentation processes and aerobic or anaerobic host cells.
WO 2012/024186 is directed to a more specific purification process wherein a composition comprising a surfactant, host cells and a bio-organic compound is heated from below to above a phase inversion temperature of the composition, thereby destabilizing the emulsion.
WO 2010/123903, US 2009/029445 and US 2012/129244 describe processes for harvesting the intracellular components from an aqueous solution comprising microorganisms, in particular algae. These processes include rupturing the cell walls of the microorganisms in order to release the intracellular components into the aqueous solution. The intracellular components can be separated from the solution by applying microbubbles and forming a foam layer, such that the intracellular components attach to the microbubbles and float upwards toward the surface of the aqueous solution. The intracellular components are recovered by separating the foam from the aqueous solution.
U.S. Pat. No. 7,960,574B1 describes a method of separating oil from oil-containing seeds, comprising aerating an aqueous dispersion of germ particles of oil-containing seeds. The aeration results in bubbles to which the oil adheres and the bubbles form a foam at the upper surface of the dispersion. The oil is recovered by separating the foam from the dispersion.
A disadvantage of WO 2010/123903, US 2009/029445, US 2012/129244 and U.S. Pat. No. 7,960,574B1 is that the product is obtained as part of a foam, such that further phase-separation (e.g. decanting, centrifugation) is still required in order to isolate the product.
It is an object of the invention to recover the liquid fermentation product from the fermentation mixture in a more efficient way by enhancing separation of the liquid product and the aqueous medium of the fermentation mixture.